Panels made of wood or wood-containing material are used nowadays in a very wide variety of applications. In order that the panels have a pleasing appearance and are adaptable to the use requirements, a flexible edge band is frequently adhesively bonded over the narrow edges, and flexible cover panels or cover bands are frequently adhesively bonded over the large areas. For example, kitchen or bathroom furniture is very frequently manufactured from such panels.
Edge banders are available for producing panels of this type. There are machines which are capable of providing the large area of the panels with cover panels or cover bands, and there are machines which are provided for only providing the narrow edges with the edge band. Machines which can carry out both processes are also known.
An apparatus for applying adhesive to a substrate is known from practice, comprising an application roller which is rotatable about an axis, a device for discharging adhesive onto a circumferential surface of the application roller, a dispensing region of the application roller for dispensing adhesive from the application roller onto the substrate, and a stripping blade, wherein the dispensing region for adhesive is arranged behind the device for discharging the adhesive onto the application roller and in front of the stripping blade in the direction of rotation of the application roller.
The device for dispensing adhesive onto the circumferential surface of the application roller is a slotted nozzle. Adhesive is applied to the application roller with the slotted nozzle in a width which corresponds to the thickness of the substrate. The length of the adhesive application to the application roller (circumferential length) corresponds to the length of the substrate multiplied by a multiplication factor. With this apparatus, it is possible to deposit only the amount of adhesive on the application roller that is required for complete gluing of the narrow edge of the substrate. The adhesive is virtually completely transferred here from the application roller onto the substrate, and only very little residual adhesive arises which has to be removed from the application roller with the stripping blade.
In the case of such a device, the application of adhesive to the substrate starts, as viewed above a line in the direction of the thickness of the substrate, with an increase to the thickness of the adhesive film and ends with a decrease in the thickness of the adhesive film toward the end of the substrate thickness. If the edge band is placed against the substrate which is provided with adhesive, less adhesive is present in the region of the increase and of the decrease, and a visible gap arises between edge band and substrate. This is not acceptable for a pleasing appearance of the coated substrate. Instead of or in addition to the gap, interruptions in the adhesive (adhesive holes) may also be visible between edge band and substrate. The interruptions in the adhesive become more greatly visible whenever the substrate is additionally painted, and water may penetrate into the substrate through said interruptions in the adhesive. These negative effects can be virtually eliminated by an application of adhesive to the application roller, the application of adhesive being slightly wider than the thickness of the substrate. However, this has the disadvantage that more adhesive has to be removed with the stripping blade and disposed of. This increases the consumption of adhesive. This also results in higher production costs and more material which is to be disposed of.
In the event of a prolonged shutdown of the edge bander, the application of adhesive to the first substrate with the apparatus is incomplete after the system is restarted. This is because the liquid adhesive runs slowly downward due to gravity in the vertically oriented slotted nozzle and, in the event of a prolonged shutdown of the system, emerges from the outlet opening in the slotted nozzle. The adhesive which has emerged is replaced in the upper region of the outlet opening by an air cushion of identical volume. The volume of the adhesive which has emerged is dependent, alongside the time, primarily on the viscosity and the geometry of the slot-shaped outlet opening of the slotted nozzle. If the edge bander is started again after a prolonged shutdown time, adhesive is lacking in the upper region during the first application of adhesive from the slotted nozzle onto the application roller, and the application of adhesive at the start of the substrate is incomplete.
The last-mentioned disadvantage is eliminated in the case of the apparatus known from practice by means of the controller of said apparatus. The controller of the apparatus has information about when a substrate is supplied. If there is an interruption in production and a substrate is not supplied, the controller starts a settable counter. If the counter has run down and no substrate has been supplied, the controller activates the flow of glue through the slotted nozzle for a brief time as soon as the controller establishes that a substrate is being supplied again. This takes place before the substrate comes into contact with the application roller for the gluing. As a result, the part filled with air in the slotted nozzle is replaced with adhesive, and a little adhesive is dispensed onto the application roller. Since said adhesive does not come into contact with the substrate, it is stripped off by the stripping blade and disposed of.
Furthermore, a slotted nozzle is known from practice in conjunction with spine coat solutions for PUR adhesive bonding of a book spine, at which slotted nozzle the slot length of the nozzle can be set in accordance with the thickness of the book spine to be adhesively bonded. The slotted nozzle has an outlet opening and a first bore running in parallel at a distance below said opening. In said first bore, a plunger rod, to which a tab which engages in the slot of the nozzle is fastened, is movable in the direction of the first bore. It forms the adjustable end of the slot length on the slotted nozzle in that the tab and the plunger are sealed off from the adhesive. The adhesive which is supplied through a second bore, which opens on the side opposite the plunger rod into the first bore, flows over the free length of the first bore and out of the slotted nozzle through the free slot when the flow of adhesive through the slotted nozzle is activated. A slotted nozzle of this type can also be used on the apparatus for gluing the narrow edge of a substrate on an edge bander. However, the previously described disadvantages occur here.
The last-mentioned slotted nozzle therefore has a nozzle body, a nozzle slot formed in the nozzle body, a passage in the nozzle body for supplying the adhesive to the nozzle slot, and a slot-shaped outlet opening of the nozzle slot.